1. Field of the Invention
The present invention relates to an aerodynamic lens, and more particularly to an improved aerodynamic lens capable of effectively focusing fine nano particles having a size of 5˜50 nm in air.
2. Description of the Related Art
Generally, an aerodynamic lens focuses particles floating in the atmosphere so as to make a particle beam, and it is adopted as an inlet of a device such as a single-particle mass spectrometer (SPMS).
As well known, the single-particle mass spectrometer analyzes chemical composition and size of a single aerosol particle.
The aerodynamic lens is used in an in-situ particle monitor (ISPM) which is able to measure particles in a vacuum in real time using light scattering of particles in order to control the pollutant in a workplace so as to enhance a production efficiency of semiconductors.
Also, the aerodynamic lens is used to project a particle beam to a target so as to deposit an article of micro-nano scale.
The conventional aerodynamic lens, as shown in FIG. 1, includes a plurality of orifices 1 arranged in a row to thereby focus aerosol particles into a beam.
However, the conventional aerodynamic lens is limited to focus particles only having a size of more than 50 nm and hundreds of nano meters.
In order to solve the above problem, Wang and his colleagues have suggested a method of focusing particles having a size of 3˜30 nm using gases of low density such as helium (He). [Wang, X., Kruis, F. E. and McMury, P. H., 2005a, “Aerodynamic Focusing of Nanoparticles: I. Guidelines for designing Aerodynamic Lenses for Nanoparticles,” Aerosol Sci. Techno., Vol. 39, pp. 611-623]
However, since the aerodynamic lens seeks for analysis of aerosol particles in atmosphere, introduction of helium to the system is not preferable. In addition, the size of the focused beam is more than 2 mm which is not suitable for analysis of particles. Also, the single-particle mass spectrometer should have a very complicated configuration to handle helium.
Another problem of the conventional aerodynamic lens is that it involves serious vortex. In FIG. 2, (a) illustrates a simulation of flow in case that the flow rate of He is 100 sccm and the inner diameter of the orifice (see 1 of FIG. 1) is 1.3 mm. As shown in the drawing, a vortex is generated behind the orifice, which prevents uniform focusing of particles.
In FIG. 2, (b) shows the stream of gas flow wherein helium is replaced with air as a carrier gas. In this case, the vortex behind the orifice is severer